1. Field of the Invention
The present invention relates generally to an electric motor and, more particularly, to an assembly of electric motor with encoder, which includes a shield grounding arrangement provided for a cable having a signal wire for outputting the detecting signal of the encoder and a shield member for shielding the signal wire.
2. Description of the Related Art
In an electric motor, an encoder provided for detecting positional data, such as the rotation angle of a motor shaft, has recently been developed so as to have detectability with higher precision and resolution, and accordingly, it is necessary to reduce the influence of noise on the output signal of the encoder sufficiently. Conventionally, for the purpose of reducing the influence of noise, a cable having therein a signal wire for outputting the detecting signal of the encoder (hereinafter referred to as an output signal cable) is provided with a shield member having a linear, network or film shape. The shield member provided in the output signal cable is generally electrically connected to the housing of the electric motor for grounding purposes.
Japanese Unexamined Patent Publication (Kokai) No. 2002-354756 (JP2002-354756A) discloses an electric motor with encoder, wherein the output signal cable of the encoder is connected to a board connector on a circuit board of the encoder through a cable connector having a grounding wire. A shield member contained in the output signal cable is connected to the housing of the electric motor, through the mutual-connecting terminals of the cable and board connectors, a patterned conductor on the circuit board and the grounding wire of the cable connector. The grounding wire is secured at the distal end thereof to the housing of the electric motor by a screw, whereby the shield member is electrically grounded.
Japanese Unexamined Patent Publication (Kokai) No. 2002-101605 (JP2002-101605A) discloses an electric motor with encoder, wherein the output signal cable of the encoder is mounted on the housing of the electric motor through an electrical-conductive bush. A shield member contained in the output signal cable is partially exposed by removing a cable sheath, and is electrically connected to the motor housing for grounding purposes, by fixing the conductive bush to the exposed portion of the shield member as well as to the motor housing.
Japanese Unexamined Patent Publication (Kokai) No. 10-239101 (JP10-239101A) discloses an electric motor with encoder, wherein a shield member provided in the lead wire of the electric motor is connected to an encoder cover. The shield member of the lead wire is electrically connected to the encoder cover for grounding purposes, by fixing the distal end of a shielding wire extending from the lead wire to the encoder cover by a screw.